1. Field of the Invention
The present invention relates to the field of solder paste stenciling, and more specifically to a solder paste stenciling apparatus for minimizing residue of solder paste.
2. Description of Related Art
Solder paste stenciling is a technique for depositing solder onto a substrate such as a printed circuit board. The purpose of doing so is when an electrical component is engaged onto the substrate, the deposited solder therebetween becomes a conductive substance that electrical connects the substrate and the electrical component together.
With reference to FIG. 9, a conventional solder paste stenciling apparatus mainly includes a stencil (70), a supporting member (72) for retaining the stencil (70) and a squeegee (73). In operation, a substrate (80) is engaged to a bottom surface of the stencil (70). Solder paste (74 shown in FIG. 10A) is applied onto a top surface of the stencil (70). The squeegee (73) is then used to level the solder paste (74) so that stencil openings (71) defined in the stencil (70) are filled with the solder paste (74) as shown in FIG. 10A. With reference to FIGS. 10B and 10C, the substrate (80) and the stencil (70) are slowly separated afterwards so that due to viscosity and gravity, most of the solder paste (74) is drawn out of the stencil openings (71) and deposited on the substrate (80). At the same time a portion of the solder paste (74) is adhered on an inner surface defining the stencil openings (71) and forms residue (75).
However, when the stencil openings (71) defined in the substrate (80) are configured to have a large aspect ratio (=depth/width), the amount of residue (75) will increase and consequently, the amount of solder paste (80) deposited will decrease. Therefore, two main problems arise from this phenomenon. Firstly, after stenciling several times, the stencil openings (71) may easily become blocked by the residue (75). Secondly, the insufficient amount of solder paste (74) deposited will effect the performance of the substrate (80) or more specifically, conductivity between the substrate (80) and an electrical component engaged thereon is impaired.
Therefore, contemporary solder paste stenciling focuses primarily on two solutions to overcome the mentioned problem. Firstly, the amount of residue (75) is reduced by slowing the separating process of the substrate (80) and the stencil (70) so that the viscosity and gravity are able to draw a lot of the solder paste (74) out of the stencil openings (71). Secondly, referring to FIG. 11, rollers (90) are used to clean the stencil openings (71), and as shown in FIG. 12, a cloth (91) and blowing means are used to urge the residue (75) out of the stencil openings (71). However, none of these methods provides a complete solution of the mentioned problem. The residue (75) still more or less adheres to the inner surface defining the stencil openings (71) after each stenciling operation.
Hence, the present invention intends to provide a solder paste stenciling apparatus for minimizing residue of solder paste.
The objective of the present invention is to provide a solder paste stenciling apparatus such that residual solder paste adhered in stencil openings of a stencil is minimized so that the number of times required to clean the stencil in order to prevent blocking of the stencil openings can be reduced if compared with a conventional stenciling apparatus of the like. Moreover, solder paste is uniformly and fully deposited on a substrate 80 that a high quality substrate can be produced.
Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
To achieve these objectives, a solder paste stenciling apparatus mainly includes a supporting member, a stencil retained on the supporting member and at least one vibrator for vibrating the stencil. The stencil has multiple stencil openings defined therein.
In operation, a substrate is engaged to a bottom surface of the stencil and solder paste is applied onto a top surface of the stencil. When the stencil and the substrate are slowly separated, the solder paste is deposited onto the substrate via the stencil openings while the at least one vibrator vibrates to minimize adhering of the solder paste in the stencil openings.